Posted by Roger L. (rogerlov@…>)
“This is another one of those “I should know but I really don’t” kind of questions. How do you track down a short?”
First some simple knowledge.
- Most shorts are physical problems - things like an abraded wire rubbing on a metal part. A short just means a bare wire touching something conductive that it shouldn’t. You can usually find them with your eyes after using a meter to get in the general area.
- Most boats are wired the same for the DC portion of the electrical system…No matter how complex the wiring looks there is simply a + and a - wire connected to every single device. It is common for all of the negatives (-) to be connected together and then for the positive (+) wire to the device to have a fuse in the line. The switch may be on a panel or in the device itself.
Below here is a plan for a simple step by step method to search for a short. It is exactly how most electrical guys do it, and if you run into problems the information will make sense to anyone. It will require a multimeter, a couple of hand tools, tape, and a flashlight. Oh… when you get the multimeter be sure to get alligator clips for it - that leaves a hand free. A ten dollar multimeter will work, but as you get better with it you are going to wish you had paid for the features of a hundred dollar one. Better yet, get both. It is worthwhile to invest in yourself.
Here we go:
First you disconnect the battery or batteries from the wires to its terminals. Leave all the wires connected to each other just as they are…but be sure to disconnect ALL of the house batteries.
Now for the multimeter. Find out how to set the dial to read “continuity” …sometimes this is known as “resistance” in an older meter…and sometimes the leads have to be plugged into specific holes in the meter to measure continuity. However you do it, set the meter that way and then test it by touching the test leads to each other to simulate a short. As you simulate the short take note whatever indication that you get from the meter… That is your clue as to what the meter considers to be a short.
Now we start isolating wires. Sometimes a wiring sketch helps too. The game is to see if any of the wires show continuity where they shouldn’t. One of the simplest and probably the first portion of the search is to connect each meter lead to one of the DISCONNECTED battery leads. It is important that every battery be disconnected from its leads when you are tracing a short. With the battery/s disconnected and the meter leads connected to the battery leads, turn the main battery switch on - just like you were getting ready to use the boat.
The meter will probably show continuity - which means that either something is shorted or else some circuit is turned on. With the meter connected up this way your next task is to run around and turn off circuits until you are convinced that everything on the boat is turned off. If you have done that and you still have continuity then you have a short somewhere. The simple way to continue the quest is to physically disconnect wiring until the short goes away. Then, having isolated the short to a single wiring harness or wiring system you begin a physical inspection looking for frayed wires or bad components. You can disconnect wiring as you trace the circuit and this enables you to divide the area where the problem is into smaller and smaller portions of the circuit.
KEEP NOTES, and take digital photos!!
This is all a simple process of “eliminate and move forward”, but there are areas where some things simply require experience. For instance, the generating circuit in the motor often contains parts that resemble shorts but really aren’t. The solution to that is to disconnect the charging wire at the engine. That way you can consider the engine as being good and the wiring is still suspect. Again, it was just a matter of divide and simplify until you find the problem. Sometimes some battery monitors, gauges, and safety device circuits cannot be turned off and will show as short even when they are working as they should. These are pretty dependable devices, so the trick there is the same as the with the generator part of the engine - disconnect the wire at the device and consider the device as good and the wiring to the device as suspect.
And I don’t know of any better way to get experience without starting out with simple - even dumb - questions.
Good Luck, Roger L. F28cc (tri)
----- Original Message -----
From: Scott Forgey
To: FreedomOwnersGroup@yahoogroups.com
Sent: Sunday, October 05, 2008 10:00 AM
Subject: RE: [FreedomOwnersGroup] Electrical Fun - Bilge
OK.
This is another one of those “I should know but I really don’t” kind of questions. How do you track down a short?
I have some ideas and am able to do some basic work, but it is time to get scientific from anyone who knows what they are doing as I stumble in the dark (without my bilge pump).
Good thing she takes on very little water. Nearly none.
Thanks.
Scott Forgey
21362 Summertrace Circle
Boca Raton, FL 33428
561.445.5179
skype: sforgey1
“Nothing is ever wrong in the universe, there is only what’s missing!”
W. Erhard
From: FreedomOwnersGroup@yahoogroups.com [mailto:FreedomOwnersGroup@yahoogroups.com] On Behalf Of Capt. HermanSent: Saturday, October 04, 2008 5:24 PMTo: FreedomOwnersGroup@yahoogroups.comSubject: Re: [FreedomOwnersGroup] Electrical Fun - Bilge
greetings…
sounds like you have a short in the wires…
track the wires from the bilge to the switch and to the batteries…making sure they aren’t worn and shorting against each other…
Capt. Herman
----- Original Message -----
From: jsforgey
To: FreedomOwnersGroup@yahoogroups.com
Sent: Saturday, October 04, 2008 4:55 PM
Subject: [FreedomOwnersGroup] Electrical Fun - Bilge
My bilge pump (Rule 1000) tripped the circuit on the panel afterhaving run my batteries down.I changed it out in a snap and installed the new one it still trips. Hmmm.I checked the float switch but dont see a problem…electricity flowsthrough it easily. What to do?Suggestions? Is it time to buy a multimeter?Bilge is pretty dry…but it would be nice to fix this quick.ScottF-32 Girlfirend
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